This invention relates, in general, to machines for cutting brittle materials, and more particularly, to wire saws for cutting semiconductor boules into semiconductor wafers.
Wire saws are used to cut semiconductor boules into semiconductor wafers. An example of a wire saw is described in U.S. Pat. No. 3,831,576 (the ""576 patent) issued on Aug. 27, 1974, invented by Harold W. Mech, and assigned to Motorola, Incorporated. FIG. 1 of the ""576 patent illustrates a wire wrapped around three pulleys. Each pulley has a wire guide and a mandrel, and each wire guide has multiple grooves. The wire is wrapped around each wire guide multiple times and is located in the multiple grooves of each of the wire guides to define a work surface or cutting area. A semiconductor boule is cut into a plurality of semiconductor wafers at the cutting area.
The assembly of each of the three pulleys is not an easy process. For example, a hydraulic press is needed to press a wire guide onto a mandrel for each pulley. The hydraulic press can produce up to ten tons of force, which is applied between the wire guide and the mandrel to install the wire guide onto the mandrel. The mandrel and the wire guide are lubricated to decrease the insertion force caused by the interference fit between the mandrel and the wire guide. The technique of pressing the wire guide onto the mandrel stretches and deforms the inside surface of the wire guide to produce a slip-free interface between the wire guide and the mandrel. This slip-free interface enables the wire guides driven by the mandrels to move the wire across the cutting area.
However, the deformation of the inside surface of the wire guide can offset the concentricity of the wire guide to the mandrel. Furthermore, it is difficult to position the wire guide on the mandrel at a precise location, and this lack of precision may result in an inaccurate cutting width. Additionally, the removal of the wire guide from the mandrel damages the inside surface of the wire guide such that the wire guide cannot be reused.
Other tools exist to cut semiconductor boules into semiconductor wafers, but these tools are significantly larger machines with wire guides measuring as much as ten times greater than those of the ""576 patent. The approach often used for these larger machines is to fabricate the wire guide in two opposing halves or xe2x80x9cclam shellsxe2x80x9d. Each of the clam shells contain pockets or counter-bore holes positioned along its longitudinal axis, and fasteners are located within these holes to hold the clam shells together. However, these features of the clam shells interrupt the grooves that hold and position the wire of the wire guide. This interruption in the grooves holding the wire may cause wire instability problems in smaller wire guides.
Accordingly, a need exists for a machine for cutting brittle materials that has pulleys, which can be assembled precisely and can be disassembled and reused without damaging the wire guides of the pulleys.